While the addition of carbon monoxide to the fill gas of incandescent lamps is shown to be beneficial to the performance of such lamps (see, for example, U.S. Pat. Nos. 3,728,572 and 3,364,376, and 4,163,171), it has heretofore been generally believed in the lighting field that the presence of elemental carbon and oxygen in the arc tube fill of metal halide high intensity discharge (HID) lamps degrades lamp performance. Carbon has been viewed as a harmful impurity which forms deposits on the arc tube walls thereby causing the light output of the lamp to diminish. Further, elemental oxygen has been viewed as an undesired fill component which reacts with the radiating species of the fill gas to form stable metal oxides. Such removal of radiating species from the fill gas degrades the radiation spectrum of the lamp.
Because of the significant and substantial differences between the chemistries of incandescent and metal halide HID lamps, the use of carbon monoxide in incandescent lamps does not and would not suggest that the addition of carbon monoxide to the arc tube fill of metal halide HID lamps would be useful.
The differences between the chemistries of incandescent and metal halide HID lamps are borne out by the following. Mercury, for example, is not useful in tungsten halogen incandescent lamps. Mercury will react with gaseous iodine present in the fill of such lamps to form solid mercury iodide compounds, thereby removing iodine from the regenerative cycle of the lamp. Mercury, on the other hand, is a typical component of the arc tube fill of a metal halide HID lamp. The mercury in metal halide HID lamps forms condensed mercury iodide compounds. Such condensed mercury iodide compounds are unique to metal halide HID lamps, and emphasize the distinction between metal halide HID lamps and incandescent types. An example of another metal which is known to be useful in metal halide HID lamps and not useful in incandescent lamps is sodium. While sodium is present in the fill of a large majority of metal halide HID lamps, sodium is known to adversely affect the regenerative cycle of the tungsten halogen incandescent type lamp. See, for example, U.S. Pat. No. 4,163,171.